1. Field: This invention relates to electrolytic techniques and apparatus for recovering silver from silver-laden fixer solutions derived from photographic and x-ray film processors.
2. Prior Art: Various apparatus and techniques are utilized for the recovery of silver from silver-laden fixer solutions from photographic film processors.
Electrolytic techniques and apparatus employed in silver recovery systems are disclosed in U.S. Pat. Nos. 3,926,768 and 3,959,110 to Burgess; 3,715,291 to Bentley; 4,139,431 to Scheidegger, et al.; 4,166,781 to Staples; 4,362,608 and 4,287,044 to Biles, et al.; 3,964,990 to Woyden; 4,111,766 to Idota, et al.; and 4,127,465 and 4,078,983 to Higgins; and in United Kingdom Pat. No. 2,067,598.
The Higgens patents are representative of electrolytic silver recovery systems associated with photographic film processors wherein current is adjusted proportionately in relation to the rate of film processed. Systems employing techniques such as those employed by Higgins require extensive electronic sensing and control circuitry.
Other systems, such as those disclosed in the Burgess patents, employ a precollection chamber into which spent fixer solution is collected. Upon collection of a predetermined volume of solution, the spent (silver-laden) fixer solution is dispensed automatically into an electrolytic cell which is full of treated (desilvered) fixer solution. The cell, however, has only one discharge port, which is an overflow port. Silver-laden solution flowing into the upper portions of the cell will tend to make the upper portions of the solution in the container silver-rich. The overflow of this silver-rich solution in the upper regions of the container will tend to occur in disproportionate amounts in comparison with the original resident low-silver solution in the container. Thus, silver will be lost to the drain without being treated due to the container's structure and the manner of introducing silver-rich solution
British Pat. No. 2,067,598 discloses a process and apparatus for recovering silver from photographic fixer solutions by electrolytic plating onto a cathode in which the plating current and a pump for withdrawing desilvered solution from the recovery tank are controlled by a timer and two liquid level switches where one switch is mounted above the other switch on the tank's side. One limitation of this apparatus involves the use of two switches, thus increasing costs and likelihood of malfunction. In order to agitate the solution, the cathode is attached to a motor by a gear train and is rotated. This attachment of the cathode to the motor makes the cathode's removal relatively difficult when the user wishes to recover the electroplated silver from the cathode. Also, in one mode, the British patent contemplates discharge of the fixer solution during desilvering, thus returning silver-bearing fixer solution to the film processing system's fixer tank. In an alternate mode, the British patent indicates operation wherein the pump is on only during discharge and is activated by a timer.